The present invention relates to cleaning brushes and in particular to electrostatic cleaning brushes for use in electrostatographic reproducing apparatus.
In electrostatographic reproducing apparatus commonly used today a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
Commercial embodiments of the above general processor have taken various forms and in particular various techniques for cleaning the photoreceptor have been used. One of the most common and commercially successful cleaning technique has been the use of a cylindrical brush with soft bristles such as rabbit fur which has suitable triboelectric characteristics. The bristles are soft so as the brush is rotated in close proximity to the photoconductive surface to be cleaned, the fibers continually wipe across the photoconductive surface to produce the desired cleaning.
Subsequent developments in cleaning techniques and apparatus in addition to relying on the physical contacting of the surface to be cleaned to remove the toner particles also rely on establishing electrostatic fields by electrically biasing one or more members of the cleaning system by establishing a field between a conductive brush and the insulative imaging surface so that the toner on the imaging surface is attracted to the brush. Thus, if the toner on the photoreceptor is positively charged then the field would be negative. The creation of the electrostatic field between the brush and imaging surface is accomplished by applying a DC voltage to the brush. Typical examples of such techniques are described in U.S. Pat. Nos. 3,572,923 to Fisher et al. and 3,722,018 to Fisher. A further refinement of these electrostatic brush cleaning devices is described in U.S. Pat. No. 4,494,863 to Laing wherein in addition to establishing an electric field between the imaging member and the brush to attract charged toner particles from the imaging member, a pair of detoning rolls, one for removing toner from the biased cleaner brush and the other for removing debris such as paper fibers and clay from the brush are provided. The two detoning rolls are electrically biased so that one of them attracts toner from the brush while the other one attracts debris thereby permitting toner to be used without degradation of copy quality while the debris can be discarded.
In all the brush cleaning systems, a balance between cleaning performance the removal of toner from a delicate imaging member, versus wearing abrasion and filming on the imaging member must be maintained at all times. The electrostatic brush techniques such as those described by Fisher, Fisher et al and Laing have the benefit in that the brush may be rotated relatively slowly and as a result the process speed may be increased while maintaining cleaning brush speed at the same relative rate. A further problem with abrasion may be present with the advent of photoconductive materials which are not as resistant to abrasion as materials of the past. For example, photoreceptors of the type disclosed in U.S. Pat. No. 4,265,990 to Stolka et al. which is directed to photoconductors comprising an electrically conductive substrate, a charge generator layer with photoconductive particles dispersed therein in an insulating organic resin and a charge transport layer are particularly susceptible to a abrasion damage by pure mechanical brush cleaners.
Initially, electrostatic brush cleaning devices employed brushes made with metal fibers such as stainless steel fibers because of their ready availability. While effective for some applications, they suffer certain deficiencies in that in addition to being relatively abrasive there is a tendency for the stainless steel fibers to entangle and compression set thereby causing premature shortfalls in cleaner performance. Furthermore, since the fibers are highly conductive if any one filament comes into contact with the ground surface, it would short out the whole brush providing a generalized cleaning failure. In addition, of course, loose fibers would short out other electrical elements such as corotrons, switches, etc. Finally, since stainless steel fibers are sold on a weight basis, they become very costly in comparison to other fibers having a much lower specific gravity. Accordingly, there has been a desire and a need to provide an alternative more economical, long life, stable fiber.